class Solution {
public:
    int climbStairs(int n) {
        if (n == 0 || n == 1) return 1;
        if (n == 2) return 2;
        vector<int>dp(n + 1);
        dp[0] = 1, dp[1] = 1, dp[2] = 2;
        for (int i = 3; i <= n; i++) {
            dp[i] = dp[i - 1]+ dp[i - 2];
        }
        return dp[n];
    }
};
